Salesforce has re-introduced URL hacks. This was something that was used a fair bit in Salesforce Classic. With the release of Saleforce Lightning, these “hacks” were no longer supported.
But thanks to Spring 20, these have been added back. The URL hack will only work with custom buttons or links.
To create a button or link which will create a new record with predefined values, use the following formula:
/lightning/o/Lead/new?defaultFieldValues=
FirstName={!Lead.FirstName},
LastName={!Lead.LastName},
LeadSource=Online+Lead,
LeadStatus=New
